Some of the strains carry the toxin Panton-Valentine Leukocidin (PVL), which attacks white blood cells, leaving the sufferer unable to fight infection.

The 18-year-old was four weeks from the end of his 32-week course at the Commando Training Centre in Lympstone, Devon, when he reportedly scratched his legs while running on 31 October last year.

He was admitted to the base medical unit, and later taken to the Royal Devon and Exeter Hospital where he died on 2 November.

A post-mortem examination showed heart and respiratory failure, and traces of PVL were later found.

His grandmother Edwina Fooks, from Bournemouth, Dorset, said: "He was dedicated to the Marines. He was doing what he wanted to do."

"I don't honestly think there was any negligence whatsoever. Who would have expected it?

"When you see these boys going on field exercises they all come back with aches and pains and blisters and things like that. You're not looking for anything like that.

"You're just caring for them and hoping they are going to get over it. You don't expect anything like this to happen".

A military Board of Inquiry set up following the recruit's death found the response of Royal Marines medical staff had been "timely and adequate", a Royal Navy spokeswoman said.

The board made recommendations for improving administrative procedures relating to next of kin but these would not have had any bearing on the teenager's death, she added.

The spokeswoman said the "disastrous" outcome of an apparently minor incident would not affect the training programme for Royal Marine recruits.

Coroner Dr Elizabeth Earland recorded a verdict of accidental death, and told the hearing she would make a recommendation to the chief medical officer to send information to all doctors, updating them on likely symptoms.